Thermal printing heads are known, for example, devices of the type having characters which are recorded on a heat sensitive paper by means of heating elements which take the form of dots or lines that come in contact with the paper. In this arrangement, the heated spots of paper form a colored reproduction of the heating element due to a chemical reaction which occurs in the surface layer of the paper. Furthermore, heating elements in the form of dots can produce a matrix print, and heating elements in the form of lines or segments may, in the same manner, produce a segment print. The construction usually incorporates a support member, and the whole assembly is called a printing head. However, it is expensive to fabricate a printing head of the type known and used in the prior art. For example, it is costly to apply diodes on a substrate according to thick-film or thin-film techniques. Furthermore, the number of supply conductors to the printing head of the prior art constructions can, of course, be reduced by mounting the drive stages directly on the printing head. However, this construction and arrangement involves great cost. Although the heating elements of the printing head can be produced by the so-called thick-film technique, in the event that diodes or drive circuits are to be utilized on the printing head, this method is also expensive.
The present invention relates to a thermal printing head with a multiplicity of electric heating elements for recording information on a heat-sensitive recording material, such as paper, the head including a support member carrying the elements and further comprising means for the selective supply of current to one or several of said heating elements.
It is an object of the present invention to produce a printing head according to the advantageous and inexpensive thick-film technique without the need of diodes or the like on the printing head.
It is a further object of the present invention to provide a thermal printing head which constitutes heating elements that are voltage-dependent resistive elements. Preferably, a current-voltage characteristic of each voltage-dependent resistive element is such that its resistivity is high at low voltages over the element.